Destructive parasite leads to mass deaths of sea urchins worldwide
A tiny, unassuming parasite is wrecking havoc on the worldwide sea urchin population: Ciliates are infecting entire regions and stripping sea urchins of their tissues in a short time. Experts are now speaking of a pandemic.
A mass die-off of sea urchins has evolved into a global pandemic. The deadly disease can now be traced in the Indian Ocean, reports a research team in the journal "Current Biology." Photos show piles of deceased sea urchins on a beach on the island of La Réunion. The outbreak poses an immediate threat to coral reefs worldwide: Sea urchins feed on algae, which would otherwise overgrow and kill corals.
A mass mortality of diademed sea urchins due to ciliates was first observed in the US Virgin Islands in January 2022. In the months afterward, similar incidents were reported in large parts of the Caribbean. The Mediterranean was hit next, followed quickly by the Red Sea.
The researchers estimate that, since December 2022, nearly all populations of the afflicted sea urchin species in the Red Sea and hundreds of thousands of sea urchins worldwide have been wiped out. For example, in the reef system near the Israeli coastal town of Eilat, the two sea urchin species that were previously the most abundant in the Gulf of Aqaba have disappeared entirely.
The team led by Omri Bronstein from Tel Aviv University has identified the pathogen behind the extinction of common diademed sea urchins (Diadema setosum) - long-spined, black sea urchins - in the Red Sea: a ciliate similar to the species Philaster apodigitiformis. This ciliate was also responsible for the mass extinction of the Atlantic diademed sea urchin (Diadema antillarum) in the Caribbean a few years ago.
Unstoppable Infections
A dramatic collapse of the population in this region was observed in 1983. The researchers note that both the coral and sea urchin populations in the Caribbean have never properly recovered. It's possible that the ciliate just identified was also involved in the mass die-off back then. According to the team, the ciliate also infects Echinothrix sea urchins, a group of species closely related to Diadema.
The parasite transforms the animals into hollow shells within two days - unless predators dine on the weakened creatures beforehand. The sinister pathogen is transmitted through water and can infest vast areas in a brief period. The stability of coral reefs is under unprecedented threat, Bronstein statement. The disease is spreading along logistical routes, as shown by data from the Red Sea.
"It's chilling to witness thousands of sea urchins on the ocean floor transform into skeletons and vanish in a very short time," Bronstein remarked. At present, there is no way to save afflicted sea urchins. Breeding populations of endangered species in isolated environments must be established so that healthy animals can later be reintroduced into the wild. Research is also required to understand the factors that led to the outbreak. One possible cause is a change in environmental conditions.
Ciliates consist of a single cell and possess cilia on their surface that enable them to move. They are frequently found in water and are often benign. However, relatives of the ciliates now found have already been implicated in mass deaths of other marine animals, such as sharks.
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The marine research community is now focused on understanding the ciliate responsible for the sea urchin deaths, as it's also linked to previous mass mortalities of Atlantic diademed sea urchins. The pandemic threatens not only the Red Sea coral reefs but also other areas where sea urchins are crucial in maintaining reef health, such as education programs in these regions could highlight the importance of marine biodiversity and the impacts of pandemics on fragile ecosystems.
Source: www.ntv.de
